Preparation of MOF Confined Ag Nanoparticles for the Highly Active, Size Selective Hydrogenation of Olefins

Article abstract of DOI:10.1002/cctc.201800744

Catalysts with both high activity and good selectivity for hydrogenation of olefins to alkanes are of interest. Herein, MOF confined ultrafine Ag NPs (Ag@HKUST-1) were synthesized by double-solvent approach using HKUST-1 as the template and support. HKUST-1 with narrow cage size distribution (0.5 to 0.9 nm) confined the growth of Ag NPs, while the uniform pores prohibited the entrance of olefins with the molecular size lager than 5.0 ?, which endow the Ag@HKUST-1 with high catalytic activity and size selectivity for hydrogenation reaction. The hydrogenation of eight kinds of olefins with different molecular size (1-hexene, cyclohexene, 1-octene, cyclooctene, styrene, 1-decene, 1, 1-diphenylethylene, and 1-dodecene) catalyzed by Ag@HKUST-1 confirmed this hypothesis. The olefins with molecular smaller than 5.0 ? were efficiently converted to the corresponding alkanes, whereas those greater than 5.0 ? exhibited extremely low conversation. The catalyst also exhibited high recycle stability in the hydrogenation of styrene.

Full text of DOI:10.1002/cctc.201800744

Accepted Article
Title: Preparation of MOF confined Ag NPs for high size selective
hydrogenation of olefins
Authors: Hong Jiang, Wen-Jing Chen, Bin-Hai Cheng, and qing-Ting
Sun
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To be cited as: ChemCatChem 10.1002/cctc.201800744
Link to VoR: http://dx.doi.org/10.1002/cctc.201800744
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Preparation of MOF confined Ag NPs for high size selective
hydrogenation of olefins
Wen-Jing Chen, Bin-Hai Cheng, Qing-Ting Sun, and Hong Jiang*
Abstract: Catalysts with both high activity and good selectivity for
hydrogenation of olefins to alkanes are of interest. Herein, MOF
confined ultrafine Ag NPs (Ag@HKUST-1) were synthesized by
double-solvent approach using HKUST-1 as the template and
support. HKUST-1 with narrow cage size distribution (0.5 to 0.9 nm)
confined the growth of Ag NPs, while the uniform pores prohibited
the entrance of olefins with the molecular size lager than 5.0 Å,
which endow the Ag@HKUST-1 with high catalytic activity and size
selectivity for hydrogenation reaction. The hydrogenation of eight
kinds of olefins with different molecular size (1-hexene, cyclohexene,
1-octene, cyclooctene, styrene, 1-decene, 1, 1-diphenylethylene,
and 1-dodecene) catalyzed by Ag@HKUST-1 confirmed this
hypothesis. The olefins with molecular smaller than 5.0 Å were
efficiently converted to the corresponding alkanes, whereas those
greater than 5.0 Å exhibited extremely low conversation. The
catalyst also exhibited high recycle stability in the hydrogenation of
styrene.
composites can be prepared either by encapsulating
presynthesized NPs in MOFs (building MOFs around the pre-
formed NPs) or using MOFs as templates to generate NPs
within their cavities.[17-19] In the former case, usually pre-
synthesized NPs are stabilized with certain surfactants, capping
agents or even ions, and NPs are then encapsulated by MOF.
NPs with different morphologies and sizes can be obtained by
controlling the synthesis conditions of encapsulation method.
However, the reported sizes of pre-synthesized NPs are usually
relatively large (~20 nm). As the hydrodynamic radius of NPs is
much larger than the cavity size of the MOF, most of NPs load
on the surface of MOF, rather than occupy the MOF cavities,
resulting low size selectivity. In the template method, the size of
NPs can be less than 10 nm, but the morphology of metal NPs is
relatively difficult to control and the obtained NPs are not uniform,
which impairs the catalytic activity.[20-23]
Double-solvent approach was developed to rationally
introduce metal precursors into MOF pores by the capillary
action and the differences in hydrophilicity inside and outside the
MOF, following reduction by H2 or other reductants to generate
tiny NPs confined in MOFs. MOFs with hydrophilic internal hole
were generally selected as host to be highly dispersed in a large
volume of low-boiling-point and non-polar organic solvent, and
then added to the metal precursor aqueous solution. Due to the
hydrophilic interactions of the MOF inner pores and the capillary
force, the metal precursor aqueous solution preferentially
diffused into the inside hydrophilic pores of the MOFs. As long
as the volume of the metal precursor is not larger than the MOF
pore volume, theoretically all metal precursors can be
completely incorporated into the MOF pores.[22, 24] For instance,
Xu et al. firstly and cleverly introduced metal precursors into the
MIL-101 (Cr) pores by the double-solvent approach and
obtained the ultrafine-sized metal NPs inside the cavities.[25]
The atom economical reactions are becoming increasingly
important for the chemical industry. Catalysts with both high
activity and good selectivity are of interest.[1-4] The size-selective
hydrogenations are critical reactions in the petro-chemical
industry whereby the molecules are absorbed in a sterically
controlled fashion and selectively transformed in the uniform
micropores, thus giving unusual product selectivity in various
reactions.[5-7] The size-selective reaction based on size or shape
selectivity has been pursued for several decades. Various types
of composite nanostructures were synthesized, typically
comprising metallic nanoparticles (NPs) embedded in or covered
by porous solid materials. The porous solid materials include a
wide variety of structures from zeolites to amorphous carbons or
porous silicon dioxide.[8-10] However, the inorganic porous
materials, such as zeolites, lack of flexibility, whereas the porous
carbon materials and the porous organic polymers are mostly
disordered in the pore structures, which possesses low
selectivity.
Herein, MOF confined Ag NPs (Ag@HKUST-1) were
synthesized by double-solvent approach using HKUST-1 as the
template and support (Scheme 1). The surface area, thermal
stability, water stability, and pore structure were detailedly
characterized. To test the catalytic activity and selectivity of
Ag@HKUST-1, eight kinds of olefins (1-hexene, cyclohexene, 1-
octene, cyclooctene, styrene, 1-decene, 1, 1-diphenylethylene,
and 1-dodecene) with different molecular sizes were
hydrogenated in the presence of Ag@HKUST-1. To our delight,
the olefins with molecular smaller than 5.0 Å exhibited excellent
conversation, whereas those greater than 5.0 Å were rarely
converted to the alkanes. After five recycles, the catalyst also
displayed excellent catalytic activity in the hydrogenation of
styrene, implying superior reusability of catalyst.
Metal-organic frameworks (MOFs) with highly uniform pore
shape and size are vitally valuable to size-selective catalysis:
when the catalyst NPs are loaded in the pores, small and
uniform reactant molecules can be accommodated and
effectively converted while molecules with large size will not be
able to contact with catalyst NPs. Furthermore, the small and
uniform pores in MOFs may confine the growth of metal NPs
during the reduction of metal ions, resulting in the uniform and
ultrafine metal NPs.[11] Meanwhile, using MOFs to confine or
stabilize the metal NPs can effectively prevent the migration and
agglomeration of metal NPs, thereby allowing the metal NPs to
exhibit superior catalytic performance.[12-16] Generally, NPs-MOF
The morphology and microstructure of HKUST-1 and
Ag@HKUST-1 crystals were investigated using SEM and TEM.
The SEM and TEM images of the HKUST-1 (Figure 1a and b)
show that octahedral crystals with diameter around 10 μm can
be obtained. The overall morphology of the 0.1 mmol
Ag@HKUST-1 (Figure 1c and d) is similar to that of the pristine
crystals even loading Ag NPs by thermal reduction at 200 oC,
[1]
W. J. Chen, B. H. Cheng, S. Q. Ting, Prof. H. Jiang
CAS Key Laboratory of Urban Pollutant Conversion, Department of
Chemistry, University of Science and Technology of China,
Hefei 230026, China
E-mail: jhong@ustc.edu.cn
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10.1002/cctc.201800744
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suggesting little damage to the framework by the thermal
treatment process. In addition, no obvious particles existed on
the external surface of the 0.1 mmol Ag@HKUST-1, indicating
that the Ag NPs were encapsulated by HKUST-1. Notably, the
edge of the HKUST-1 shown in Figure 1d was smoothly and
without impurities at the scale of 50 nm, implying the HKUST-1
crystals grow well.
Ag NPs are completely different, resulting in different size-
selective catalytic effects for hydrogenation.
Figure 2 shows the N2 adsorption-desorption isotherms and
pore size distribution profiles of HKUST-1. The adsorption-
desorption isotherm (Figure 2a) displayed a type I shape with
high N2 uptakes at relatively low pressures, indicating
a
characteristic microporous material. The specific surface area
calculated by the Brunauer-Emmett-Teller (BET) method was
1145 m2/g, and the total pore volume was 0.6476 cm3/g. As
shown in Figure 2b, pore size distribution curve of HKUST-1
analyzed by the nonlocal density functional theory (NLDFT)
algorithm exhibited the maximum peaks at 0.5 and 0.9 nm. The
3D unit cell crystal framework of HKUST-1 is composed of
square-shaped pores (diameter 9.0 Å) surrounded by small
pockets (diameter 5.0 Å) (Figure S2). The pore size distribution
of HKUST-1 is consistent with the reported literature.[26] The
slightly decreased surface area (851 m2/g) of 0.1 mmol
Ag@HKUST-1 compared with parent HKUST-1 suggests that
the cavities of the HKUST-1 frameworks are occupied by the
highly dispersed Ag NPs (Figure S3). The pore size distribution
of 0.1 mmol Ag@HKUST-1 is similar to HKUST-1, indicating the
pore structure of HKUST-1 is maintained during the loading of
Ag NPs.
Scheme 1 Schematic illustration of the synthesis process of the
Ag@HKUST-1.
As clearly seen from the TEM images and histograms of
0.05 mmol Ag@HKUST-1 and 0.1 mmol Ag@HKUST-1 (Figure
1e and f), there is no aggregation of Ag NPs, and large particles
of Ag could hardly be seen in the wide range, indicating that Ag
NPs are evenly dispersed. The average diameter of Ag NPs
increases from 2.0 to 2.5 nm and the particle size distribution is
also found to be narrow with the increase of the Ag dosages
from 0.05 to 0.1 mmol. Noticeably, TEM images clearly show the
Ag NPs are uniformly distributed in the network of HKUST-1 for
Ag@HKUST-1 (Figure 1e and f). In addition, few Ag NPs exist
on the edges of the HKUST-1, which confirms that Ag NPs have
been embedded in the inner network of HKUST-1, and not been
adsorbed on the external surface of HKUST-1. With the further
increase of Ag dosage, the Ag NP size of 0.2 mmol
Ag@HKUST-1 increased to diameter of 5.5 ± 1.2 nm (Figure 1g),
and was larger than those of the above two due to the NPs tend
to aggregation at high concentration. Most of the Ag NPs were
limited in the interior of the HKUST-1 even though a small
percentage of the NPs broke the framework and distributed on
the edge of HKUST-1. However, for the 0.1 mmol Ag-HKUST-1
prepared by a traditionally impregnated process, most of the Ag
NPs were adsorbed on the surface of HKUST-1, and some of Ag
NPs randomly distributed on the surface and inner space of
HKUST-1 after the thermal reduction. The particle size of Ag
NPs is 19.2 ± 9.2 nm, showing that the aggregation of Ag NPs
occurs during the thermal reduction process. Comparing Figure
1f and h with same Ag dosage and using double-solvents and
impregnated method, respectively, the size and distribution of
Figure 1 SEM images of (a) HKUST-1 and (c) 0.1 mmol Ag@HKUST-1;
(b) and (d) TEM images of HKUST-1 with different scales; Representative
TEM images of 0.05 mmol Ag@HKUST-1(e), 0.1 mmol Ag@HKUST-1 (f),
0.2 mmol Ag@HKUST-1 (g); and 0.1 mmol Ag-HKUST-1 (h); inset (e-h) is
the corresponding size distribution histograms of Ag NPs.
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X-ray diffraction (XRD) was performed to verify the
crystalline structure. Figure 2c shows the XRD pattern of
HKUST-1 before and after thermal reduction. All the diffraction
peaks of HKUST-1 in this study was essentially identical to that
of previously reported results.[27, 28] Further, the main diffraction
peaks remained unchanged after thermal reduction at 200 oC
under flowing H2/Ar gas, clearly indicating that the crystal
structure have not been destroyed, which is in agreement with
the result of SEM. As shown in Figure 2d, the appearance of Ag
diffraction peaks (JCPDS card no. 04-0783) suggests the
formation of Ag NPs confined by HKUST-1. The characteristic
peak of Ag at 2θ of 43.4o were observed in all Ag@HKUST-1,
which can be attribute to (200) lattice plane of Ag with a face-
centered cubic crystal structure.[29] Another characteristic peak
of Ag at 2θ of 38.3o (111) weakened and dispeared with the
decrease of Ag dosages. For 0.1 mmol Ag-HKUST-1, the
diffraction peak only appeared at 38.3o. indicating the only
existence of (111) crystal face. Besides, all the diffraction peaks
in the 2θ range of 5-30o are in good agreement with HKUST-1
(Figure 2d), which means the integrity of the HKUST-1 was
maintained after Ag loading.
be deconvoluted into two peaks with binding energies of 531.81
and 532.55 eV, one from -C=O/-OH and the other from C-O-
Cu.[33] In addition, the relative content of major elements and the
XPS survey spectra are displayed in Table S1 and Figure S4,
and the contents of Ag NPs on the surface of 0.1mmol
Ag@HKUST-1 is very low.
The thermal stability of HKUST-1 and Ag@HKUST-1 were
studied by thermogravimetric analysis (TGA) from room
o
o
temperature to 700 C with a heating rate of 10 C/min, and the
result was shown in Figure 4a, and the Derivative-
Thermogravimetry (DTG) was displayed in Figure S5. The
weight loss behavior of HKUST-1 and Ag@HKUST-1 can be
divided into two major steps. The first weight loss stage occurs
at temperatures below 130 oC, which are associated with the
loss of free molecules physically absorbed in the micropores and
the weight loss depends on the initial degree of solvation of the
materials. Comparing with the HKUST-1, the weight loss ratio of
the Ag@HKUST-1 was only 11.33% as most water and solvent
molecules were removed from the surface and pores of HKUST-
1 during the thermal reduction at 200 oC under flowing H2/Ar gas.
Notably, for HKUST-1 and Ag@HKUST-1, a platform stage can
be observed after the removal of solvent, indicating the stability
of the frameworks of the HKUST-1 crystals in this temperature
range. The 0.01 mmol Ag@HKUST-1 has a slightly different
o
onset decomposition temperature (125 C) from HKUST-1 (130
oC). The second weight loss begins at 315 oC for HKUST-1
crystals and ends around 370 oC, while the onset decomposition
o
temperature of the Ag@HKUST-1 is approximately 35 C lower
than that of the HKUST-1. This phenomenon may be caused by
the decomposition of organic ligands expedited by the small-size
and active Ag NPs.[34] The organic frameworks are initially
decomposed at 370 oC and completely carbonized at higher
temperature under N2 atmosphere. TGA analysis indicates that
using low-temperature thermal reduction at 200 oC under flowing
H2/Ar gas can obtain Ag NPs while effectively maintains the
structure of the HKUST-1.
Figure 2 (a) N2 adsorption-desorption isotherms and (b) pore diameter
distribution profiles of HKUST-1. (c) XRD patterns of HKUST-1 before
and after thermal reduction; (d) XRD patterns of Ag supported by
HKUST-1 with different methods and concentration of Ag.
Figure 3 shows the chemical composition in Ag@HKUST-1
as determined by XPS. Two characteristic peaks (Figure 3a) are
observed at 933.20 and 953.14 eV, corresponding to the Cu
2p3/2 and Cu 2p1/2 states of Cu2+, respectively.[30] In addition, the
“shake-up-satellites” located at 939.95, 943.83, and 962.46 eV,
indicating the presence of divalent Cu (II) species.[31] As shown
in Figure 3b, the two peaks at 368.53 and 374.64 eV with a spin-
orbit separation of 6.0 eV, correspond to the binding energies of
Ag 3d5/2 and Ag 3d3/2. These two characteristic peaks of Ag 3d5/2
and Ag 3d3/2 are attributed to the Ag0 species,[32] which clearly
indicates the presence of zero-valent metallic Ag NPs and is
consistent with the XRD results. The energy spectrum of
electron C 1s reveal two surface components (Figure 3c). The
peak at 284.81 and 288.65 eV are assigned to the binding
energy value of the hydrocarbon C-C and the carboxylate
carbon -COO, respectively. The peak of O 1s (Figure 3d) could
Figure 3 XPS spectra of the Ag@HKUST-1. (a) Cu 2p spectra; (b) Ag 3d
spectra; (c) C 1s spectra; (d) O 1s spectra.
Hydrogen temperature-programmed reduction (H2-TPR)
was employed to study the reductive behavior of HKUST-1-
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supported Ag ions. Combined with the TGA curves (Figure 4a),
the upper critical temperature of TPR measurement was set to
280 °C to prevent the decomposition of the HKUST-1. From
Figure 4b, no noticeable peak in pure HKUST-1 was detected,
indicating the stability of the HKUST-1 under the reduced
interesting phenomenon can be explained from Figure 1g. While
most of the Ag NPs were limited in the interior of the HKUST-1,
a small percentage of the Ag NPs located at the edge breaking
the framework. The small amounts of Ag NPs appearing on the
surface of HKUST-1 can provide low catalytic activity for large
size olefins such as 1-decene, cyclooctene, diphenylethylene,
and 1-dodecene.
o
atmosphere (H2-Ar mixture gas) in the range of 30-280 C. As
displayed in Figure 4b, 0.1 mmol Ag+-HKUST-1 shows only one
reduction peak at 210 °C which is attributed to the reduction of
monovalence Ag species to metallic Ag.[35] Similar to 0.1 mmol
Ag+-HKUST-1, 0.05 mmol Ag+@HKUST-1, 0.1 mmol
Ag+@HKUST-1, and 0.2 mmol Ag+@HKUST-1 also show a
o
broad peak in the range of 130-230 C located around a central
peak of 205 oC corresponded to the Ag+ → Ag0 reduction.
Considering the results of the TGA and H2-TPR, the low-
o
temperature thermal reduction of Ag ions to Ag NPs at 200 C
under flowing H2/Ar is reasonable and effective. While Ag ions
were reduced to Ag NPs, the structure of the HKUST-1 was
retained, which is conducive to obtain small diameter of Ag NPs
with high activity and large molecular sieving capability. These
results can be confirmed by XRD, SEM, and TEM analyses.
Figure 4 (a) TGA curves of HKUST-1 and 0.1 mmol Ag@HKUST-1; (b)
H2-TPR of HKUST-1, 0.1 mmol Ag+-HKUST-1, 0.05 mmol Ag+@HKUST-
1, 0.1 mmol Ag+@HKUST-1 and 0.2 mmol Ag+@HKUST-1.
HKUST-1 is a microporous material with uniform pores and
unique porous channel, while the Ag NPs with small diameter
exhibit excellent catalytic performance for hydrogenation.
Combining the catalytic property of Ag NPs and the molecular
sieving capability of HKUST-1, Ag@HKUST-1 may possess
size-selective property. The size-selective catalytic property of
HKUST-1 confined Ag NPs were tested in the hydrogenation of
alkenes with different molecular diameters. As shown in Figure
5a, compared with eight different olefins, the hydrogenation
efficiency displays
a great diversity. All of Ag@HKUST-1
catalysts exhibit excellent catalytic performance to the
hydrogenation of 1-hexene, 1-octene, cyclohexene and styrene,
and the hydrogenation conversion rate increases with the
increase of Ag content in the catalysts, suggesting the active site
is a dominant factor for hydrogenation. However, an obvious
difference was observed in the hydrogenation of 1-decene,
cyclooctene, diphenylethylene and 1-dodecene by different
Ag@HKUST-1 catalysts. 0.05 mmol Ag@HKUST-1 and 0.1
mmol Ag@HKUST-1 exhibit extremely low catalytic activity for
hydrogenation of these olefins, which may be mainly attributed
to the difference in the molecular size of the reaction substrate.
The structure diagram and molecular size of olefins were listed
in Table S2. It is strange that the 0.2 mmol Ag@HKUST-1
shows 13% conversion for 1-decene, 11% for cyclooctene, 4%
for diphenylethylene, and 10% for 1-dodecene under the same
catalytic condition and the content of reaction substrates. This
Figure 5 (a) Catalytic performance of Ag@HKUST-1 for the liquid-
phase hydrogenation of different olefins; (b) Catalytic performance of
Ag-HKUST-1 and Ag@HKUST-1 for the liquid-phase hydrogenation of
different olefins; (c) Reusability of 0.1 mmol Ag@HKUST-1. Reaction
conditions: 1 mmol styrene, 10 mL of CH3OH, 1 MPa H2 at 100 oC for 3
h with magnetic stirring. Color code: 0.05 mmol Ag@HKUST-1 (gray),
0.1 mmol Ag@HKUST-1 (red), 0.1 mmol Ag-HKUST-1 (black), 0.2
mmol Ag@HKUST-1 (blue).
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In order to demonstrate the size-selective catalytic
properties of the 0.1 mmol Ag@HKUST-1 synthesized by
double-solvents method, the 0.1 mmol Ag-HKUST-1 prepared
by an impregnated process was also tested in liquid-phase
hydrogenation of olefins with different molecular sizes. Under
the same reaction conditions, the 0.1 mmol Ag-HKUST-1 can
catalytically convert 70-90% of seven olefins except
diphenylethylene (9% conversion) to corresponding alkanes
(Figure 5b). The extremely low conversion of diphenylethylene is
mainly due to its conjugation effect which increases the difficulty
of hydrogenation. It shows that Ag-HKUST-1 has no catalytic
selectivity for the hydrogenation of olefins with different sizes.
Furthermore, the conversion of 1-hexene, 1-octene,
cyclohexene, and styrene by 0.1 mmol Ag-HKUST-1 is lower
than that by 0.1 mmol Ag@HKUST-1. It is mainly ascribed to the
much smaller size of Ag NPs in 0.1 mmol Ag@HKUST-1 (2.5
nm) compared to that in 0.1 mmol Ag-HKUST-1 (19.2 nm),
which exhibit higher hydrogenation activity. The randomly
distributed Ag NPs on the surface of 0.1 mmol Ag-HKUST-1 can
provide hydrogenation activity sites for large-sized olefins (1-
decene, cyclooctene, diphenylethylene, and 1-dodecene), and
thus exhibit high conversion rate for these olefins. In contrast,
the Ag NPs embedded in the inner network of HKUST-1 are not
able to interact with large-size olefins, therefore the conversion
rates of these olefins by 0.1 mmol Ag@HKUST-1 are very low.
These results clearly demonstrate the molecular size-selective
property of the 0.1 mmol Ag@HKUST-1. To further confirm the
activity of Ag NPs on HKUST-1, the initial turnover frequency
(TOF) value of the catalysts with different synthesis method is
calculated (Table S3). The TOF of 0.1 mmol Ag@HKUST-1 (120
h-1) is higher than that of 0.1 mmol Ag-HKUST-1, which may
attributed to the ultrafine Ag NPs confined in HKUST-1.
Compared with other noble metal catalysts, the catalyst of 0.1
mmol Ag@HKUST-1 has outstanding catalytic efficiency relative
to cost. To demonstrate the effect of confined pores of HKUST-1
on the selective hydrogenation of olefins, Ag NPs-C obtained by
the same conditions as HKUST-1 was also used for the
hydrogenation of olefins. It can be clearly seen from the Figure
S6 that the hydrogenation conversion of HKUST-1 is low. The
Ag NPs-C as hydrogenation catalyst exhibits good catalytic
performance for olefins except diphenylethylene due to the
active Ag NPs (Figure S6). However, compared with 0.1 mmol
Ag@HKUST-1, the Ag NPs-C exhibits low catalytic selectivity for
1-decene, cyclooctene, diphenylethylene, and 1-dodecene. In
addition, the catalytic activity of the Ag NPs-C is not as good as
that of 0.1mmol Ag@HKUST-1. This indicates that the confined
pore of HKUST-1 played an important role in the selective
hydrogenation of olefins.
HKUST-1 has large pores of 9.0 Å which are accessible
through small apertures of 5.0 Å.[22] The uniform pore
distributions could afford the ability of molecular size-selective
catalysis. Eight kinds of olefins were divided into two groups
according to whether the molecular size is greater than 5.0 Å.
The molecular sizes of 1-hexene, 1-octene, cyclohexene, and
styrene are smaller than 5.0 Å, and the group of olefins are
small enough to diffuse through the pore apertures of HKUST-1
(5.0 Å) without serious hindrance; however, another group of
olefins (1-decene, cyclooctene, diphenylethylene, and 1-
dodecene) are much bigger than the pore apertures. Therefore,
the hydrogenation conversion of two groups was significantly
different by the 0.1 mmol Ag@HKUST-1. The Ag NPs
synthesized by double-solvents method possess small and
uniform size, which endow them high catalytic activity for
hydrogenation of olefins. Meanwhile, these Ag NPs are confined
in the interior of the HKUST-1, which could improve the stability
and reusability of the catalyst.
The recycling test using styrene as model reactant was
conducted to demonstrate the stability of 0.1 mmol Ag@HKUST-
1 without any post treatment (Figure 5c). In the initial three
cycles, sufficient catalytic activity could be preserved and
styrene can be nearly completely converted (>99%). After five
recycles, the catalytic performance slightly decreased until to
seventh run, indicating that 0.1 mmol Ag@HKUST-1 has good
reusability. Loss of the active component is a main cause of
catalyst deactivation in liquid phase reactions. The high catalytic
performance of 0.1 mmol Ag@HKUST-1 was maintained after
two times of reuse, but decreased after six times of reuse.
During the recycling, the intensity of peaks of metallic Ag
decreased (Figure S8a), suggesting the leaching of the active
metal. After six times of reuse (seven cycles), the Ag content in
catalyst droped from 3.2 wt% to 1.8 wt% (Figure S8b),
coinciding with the XRD analysis.
In summary, we successfully prepared the ultrafine Ag NPs
confined by HKUST-1 using double-solvent approach and the
as-prepared catalyst exhibited much higher catalytic activity and
selectivity for hydrogenation of olefins than Ag-HKUST-1
prepared by impregnated process. The olefins with molecular
smaller than 5.0
Å
were efficiently converted to the
corresponding alkanes by Ag@HKUST-1, whereas those
greater than 5.0 Å exhibited extremely low conversation. The
catalytic performance of Ag@HKUST-1 slightly decreased using
styrene as model reactant after five recycles, indicating that
catalyst has good reusability.
Experimental section
Leaching of active components in the reaction liquid should
be taken into consideration, which relates to the homogeneous
and heterogeneous catalysis. The reaction mixture was hot
filtered by centrifugation from the mixture after 1 h of reaction,
the conversion of styrene did not increase during the
subsequent reaction under the same catalytic conditions,
indicating that no leaching of the catalyst occurred and the
process is truly heterogeneous (Figure S7).
The materials and methods are discribed in Supporting
Information.
Acknowledgements
The authors gratefully acknowledge financial support from National
Natural Science Foundation of China (21677138), Program for
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[32] W. J. Liu, L. L. Ling, Y. Y. Wang, H. He, Y. R. He, H. Q. Yu, H. Jiang,
Environ. Sci.: Nano 2016, 3, 745-753.
Changjiang Scholars and Innovative Research Team in University
“PCSIRT, the Key Special Program on the S&T for the Pollution
Control, and Treatment of Water Bodies (No.2012ZX07103−001).
[32] G. W. Zhan, H. C. Zeng, Adv. Funct. Mater. 2016, 26, 3268-3281.
[34] S. X. Gao, N. Zhao, M. H. Shu, S. N. Che, Appl. Catal. A. 2010, 388,
196-201.
Keywords: HKUST-1 • Ag NPs • double-solvents method • size-
[35] X. L. Deng, M. X. Li, J. Zhang, X. Y. Hu, J. B. Zheng, N. W. Zhang, B. H.
Chen, Chem. Eng. J. 2017, 1, 544-555.
selective • hydrogenation
[1] S. G. Modha, M. F. Greaney, J. Am. Chem. Soc. 2015, 137, 1416-1419.
[2] S. Prakash, K. Muralirajian, C. H. Cheng, Angew. Chem. Int. Edit. 2016,
55, 1844-1848
[3] M. Dhiman, V. Polshettiwar, J. Mater. Chem. A 2016, 4, 12416-12424.
[4] H. Sun, Z. G. Liu, S. Chen, X. Quan, Chem. Eng. J. 2015, 15, 889-896.
[5] S. Aguado, S. E. Jamal, F. Meunier, J. Canivet, D. Farrusseng, Chem.
Commun. 2016, 52, 7161-7163.
[6] W. N. Zhang, G. Lu, C. L. Cui, Y. Y. Liu, S. Z. Li, W. J. Yan, C. Xing, Y. R.
Chi, Y. H. Yang, F. Huo, Adv. Mater. 2014, 25, 4056-4060.
[7] L. N. Chen, H. Q. Li, M. W. Yan, C. F. Yuan, W. W. Zhan, Y. Q. Jiang, Z.
X. Xie, Q. Kuang, L. S. Zheng, Small 2017, 13, 1700683.
[8] T. M. Lima, C. G. S. Lima, A. K. Rathi, M. B. Gawande, J. Tucek, E. A. U.
González, R. Zbořil, M. W. Paixão, R. S. Varma, Green Chem. 2016, 18,
5586-5593.
[9] F. Wang, C. Liu, G. Liu, W. X. Li, J. H. Liu, Catal. Commun. 2015, 2, 142-
146.
[10] J. Zhang, L. Wang, Y. Shao, Y. Wang, B. C. Gates, F. S. Xiao, Angew.
Chem. Int. Ed. 2017, 56, 9747-9751.
[11] Q. L. Zhu, Q. Xu, Chem. Soc. Rev. 2014, 43, 5468-5512.
[12] C. B. He, D. M. Liu, W. B. Lin, Chem. Rev. 2015, 115, 11079-11108.
[13] G. W. Xu, Y. P. Wu, W. W. Dong, J. Zhao, X. Q. Wu, D. S. Li, Q. C.
Zhang, Small 2017, 13, 1602996.
[14] J. W. Zhang, C. C. Zhao, Y. P. Zhao, H. Q. Xu, Z. Y. Du and H. L. Jiang,
CrystEngComm 2014, 16, 6635-6644.
[15] J. Liang, Z. Liang, R. Zou, Y. L. Zhao, Adv. Mater. 2017, 29, 1701139.
[16] Y. P. Wu, G. W. Xu, W. W. Dong, J. Zhao, D. S. Li, J. Zhang, X. H. Bu,
Inorg. Chem. 2017, 56, 1402-1411.
[17] G. Lu, S. Z. Li, Z. Guo, O. K. Farha, B. G. Hauser, X. Y. Qi, Y. Wang, X.
Wang, S. Y. Han, X. G. Liu, J. S. DuChene, H. Zhang, Q. C. Zhang, X. D.
Chen, J. Ma, S. C. J. Loo, W. D. Wei, Y. H. Yang, J. T. Hupp, F. W. Huo,
Nat. Chem. 2012, 4, 310-316.
[18] M. T. Zhao, K. Yuan, Y. Wang, G. D. Li, J. Guo, L. Gu, W. P. Hu, H. J.
Zhao, Z. Y. Tang, Nature 2016, 539, 76-80.
[19] L. Y. Chen, R. Luque, Y. W. Li, Chem. Soc. Rev. 2017, 46, 4614-4630.
[20] Q. H. Yang, Q. Xu, S. H. Yu, H. L. Jiang, Angew. Chem. Int. Ed. 2016,
55, 3685-3689.
[21] S. Hermes, M. K. Schröter, R. Schmid, L. Khodeir, M. Muhler, A. Tissler,
R. W. Fischer, R. A. Fischer, Angew. Chem. Int. Ed. 2005, 44, 6237-
6241.
[22] Q. H. Yang, Q. Xu, H. L. Jiang, Chem. Soc. Rev. 2017, 46, 4774-4808.
[23] X. H. Liu, J. G. Ma, Z. Niu, G. M. Yang, P. Cheng, Angew. Chem. Int. Ed.
2015, 54, 988-991.
[24] Y. Z. Chen, Q. Xu, S. H. Yu, H. L. Jiang, Small 2015, 11, 71-76.
[25] A. Aijaz, A. Karkamkar, Y. J. Choi, N. Tsumori, E. Ronnebro, T. Autrey,
H. Shioyama, Q. Xu, J. Am. Chem. Soc. 2012, 134, 13926-13929.
[26]
Y. Yang, P. Shukla, S. B. Wang, V. Rudolph, X. M. Chen, Z. H. Zhu,
RSC Adv. 2013, 3, 17065-17072.
[27]
L. He, L. F. Dumee, D. Liu, L. Velleman, F. H. She, C. Banos, J. B.
Davies, L. X. Kong, RSC Adv. 2015, 5, 10707-10715.
[28] M. Mazaj, T. Čendak, G. Buscarino, M. Todaro, N. Z. Logar, J. Mater.
Chem. A 2017, 5, 22305-22315.
[29] K. Tian, W. J. Liu, H. Jiang, ACS Sustainable Chem. Eng. 2015, 3, 269-
276.
[30] Y. T. Wang, Y. Y. Lu, W. W. Zhan, Z. X. Xie, Q. Kuang, L. S. Zheng, J.
Mater. Chem. A 2015, 3, 12796-12803.
[31] E. G. Garrido-Ramírez, J. F. Marco, N. Escalona, M. S. Ureta-Zañartu,
Micropor. Mesopor. Mat. 2016, 22, 303-311.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201800744
ChemCatChem
COMMUNICATION
Wen-Jing Chen, Xiao-Qing Liu,
Shun Zhang, and Hong Jiang*
The synthesis of Ag NPs
confined by MOF (Ag@HKUST-
1) using double-solvent approach
using HKUST-1, and applied it for
size-selective hydrogenation of
olefins.
Page No. – Page No.
Preparation of MOF confined
Ag NPs with narrow cage size
distribution for high size
selective hydrogenation of
olefins
This article is protected by copyright. All rights reserved.